Project Summary Chronic tendon injury and tendinopathy are extremely common and painful degenerative conditions whose prevalence reaches 30-50% in adults over 60. Most of these people don?t seek surgical treatment, however they do receive injections or physical therapy to improve pain management and regain a small amount of strength. There are no non-surgical tendinopathy therapies that are proven clinically effective, therefore there is an urgent clinical need for the development of novel therapies for this condition. Adult stem cells are characterized by their self-renewing capacity and multipotency making them attractive starting materials for tendon, and ligament tissue engineering and regenerative medicine applications. However stem cells do not necessarily repair tissue by differentiating into the desired tissue type, but act more in a regulatory role. This is accomplished through paracrine effects and cell-cell interactions which can be carried out via secreted extracellular vesicles, including exosomes. If many of the regenerative properties of stem cells can be credited to exosomes, there will be a paradigm shift in how we view regenerative medicine and therapeutics for many indications: live cell therapies could be replaced with exosome-based biologics. Our focus is to determine the feasibility of using stem cell derived exosomes that have been specifically tuned to break the ineffective repair cycle inherent in tendinopathy. Proteomic and genomic analysis of exosome content has revealed a broad range of signaling factors that are both cell type-specific as well as differentially regulated by the secreting cells? environment. Based on these phenomena, this Phase I program is intended to address two hypotheses: 1) the cargo of stem cell-derived exosomes can be ?tuned? toward pro-healing factors by altering the cells? environment and 2) these pro-healing exosomes can be used as a potential tendon healing/regenerative therapeutic. We have developed a bioreactor-based production system for manufacturing exosomes from various cell types, including stem cells. The bioreactor is an ideal system to test exosome cargo tunability, providing a defined environment and optimized exosome purification capabilities. This Phase 1 project is designed to provide in vitro and in vivo evidence for the further development of this therapeutic approach. We will assess the healing potential of stem cell exosomes derived from two unique tissue sources using our established tenocyte culture system. This information will provide the basis to test the most effective exosomes in a rat tendon healing model. Successful results will lead to further development, mechanistic studies, age- related effects and in vivo efficacy assessments in other tendon healing models leading to our ultimate goal of developing an allogeneic therapy for chronic tendinopathy and acute tendon healing.